Amid regal pomp at Queen Elizabeth II's Windsor Castle home and thunderous applause from British lawmakers, Ireland's president began a state visit to Britain laden with symbolism for two nations that share a troubled history.

President Michael D. Higgins is making his country's first state visit to Britain since Ireland's hard-fought independence nearly a century ago. His trip underscores how much Northern Ireland's peace process has transformed relations between the two longtime adversaries since the 1990s, when IRA car bombs were still detonating in London.

Higgins, delivering the first speech by an Irish president to the joint Houses of Parliament, said Tuesday that both nations had attained "a closeness and warmth that once seemed unachievable."

Previous Irish presidents had toured England and met the queen in several official trips since 1993 as part of early peacemaking efforts. But a formal state visit with full honors had been repeatedly postponed because of security and diplomatic sensitivities.

Higgins, a left-wing politician, poet and human rights activist who was elected to the ceremonial post in 2011, said the two nations' relationship had gone "from the doubting eyes of estrangement to the trusting eyes of partnership and, in recent years, to the welcoming eyes of friendship."

"Our two countries can take immense pride in the progress of the cause of peace in Northern Ireland," he said. "There is of course still a road to be traveled, the road of a lasting and creative reconciliation."

Earlier, a military band played Ireland's martial national anthem, "The Soldier's Song," as the queen and her husband Prince Philip welcomed Higgins and his wife, Sabina, into the castle quadrangle. Outside, Irish tricolors and Union Jacks lined the streets of Windsor for the start of Higgins' four-day tour of England.

The most striking symbolism was coming later Tuesday at a Windsor Castle banquet hosted by the queen.

Among the 160 invited guests is Martin McGuinness, once a senior Irish Republican Army commander, now deputy leader of Northern Ireland's unity government. His presence at the queen's table would have been unthinkable even a few years ago.

More than 3,600 people were killed during the four-decade conflict over Northern Ireland. The main faction of the IRA killed nearly 1,800 people - among them the queen's cousin, Lord Louis Mountbatten -during its failed effort to force Northern Ireland out of the United Kingdom. Experts say McGuinness was the IRA's chief of staff when the group assassinated Mountbatten in 1979.

Another 1,000 people were killed by Protestant militants and about 360 by British security forces.

Higgins paid silent tribute to Mountbatten, and to Britain's dead from the two World Wars, during a tour of Westminster Abbey.

First he laid an Irish tricolor-decorated wreath at the tomb of Britain's "unknown warrior," the remains of a soldier retrieved from a Belgian battlefield at the end of World War I, a fight that Ireland joined as part of the UK. Ireland angered Britain by remaining neutral in World War II.

Higgins bowed his head and prayed before a monument dedicated to an unknown soldier who sacrificed his life "for God, for King and country, for loved ones, home and Empire, for the sacred cause of justice and the freedom of the world."

Then he and his wife paused at a plaque on the abbey floor honoring Mountbatten, a World War II hero who was Britain's last viceroy to India. The 79-year-old shunned personal security when holidaying in the Republic of Ireland; an IRA remote-control bomb killed him, two teenage boys and an 83-year-old woman.

Much has changed since an IRA cease-fire and the U.S.-brokered Good Friday peace accord in 1998. McGuinness' Irish nationalist party, Sinn Fein, represents most of the Irish Catholic minority in its 7-year-old coalition with British Protestants.

In 2011, the queen became the first reigning British monarch to visit Ireland since 1911, when Ireland was still ruled by Britain. The following year, she and McGuinness shook hands in a brief but minutely choreographed meeting in Belfast.

For all its symbolism of reconciliation, McGuinness' invitation to the royal banquet dismayed some IRA victims.

Stephen Gault, whose father was one of 11 Protestant civilians killed in an IRA bombing in 1987, said it was "another nail in the coffin of the innocent victims of terrorism."

Gault told the BBC he "would like to see Mr. McGuinness behind bars for his crimes."

"Yes, we all want peace, but peace at what cost? It's been a dirty peace so far," he said.